Polyethylene films and wax coatings, which are generally laminated or coated to paper, are widely used in packaging applications to protect products from moisture and provide water or grease resistance. However, recycling of packaging containing polyethylene films and wax coatings are limited and costly since special equipment is necessary for repulping and various process steps are required prior to reintroducing such a slurry into a recycling stream along with office waste paper. In addition, polyethylene films and some wax coatings will not degrade if the package is composted. These problems are encountered in specific packaging application areas, for example, where such coatings are used in the production of ream wrap.
Conventional ream wraps are typically a multi-ply product having a center ply of polyethylene in between two ply's of paper. Polyethylene is used in ream wraps to provide an effective barrier to water vapor (humidity) which can cause the wrapped paper to curl resulting in misfeeds and jams in copy machines or printing presses. These multilayered plastic film ream wraps cannot easily be recycled. Landfills and incineration are the common ways to dispose of polyethylene packaging materials. Alternatively, other coatings and coating systems are known which do not contain polyethylene but provide the level of moisture resistance necessary for ream wrap. For example, U.S. Pat. No. 4,117,199 to Gotoh et al. discloses a repulpable coated paper containing a synthetic rubber latex and a wax emulsion. Coatings such as Vapo-Stop, manufactured by Cham-Tenero Paper Mills, Inc., Cham, Switzerland, include a styrene-butadiene polymer, wax and acrylic polymer components which provide moisture resistance to coated substrates. These systems however contain a high loading of wax which make the formulation unacceptable for recycling as office waste and repulping for white paper production.
Thus it would be desirable to find an alternative for conventional polyethylene films and coatings containing wax that has comparable moisture barrier properties but also has the added benefit of repulpability and recyclablity.
U.S. Pat. No. 2,392,972 to Cheyney discloses surfacing of paper with a coating of vinylidene chloride-vinyl chloride copolymers to produce a coated paper which is resistant to the transmission of water vapor. Other representative patents which describe use of polyvinylidene chloride as a means for imparting water vapor resistance to paper include U.S. Pat. No. 3,476,587 to Demol et al. which discloses compositions comprising two vinylidene chloride copolymers, one hard and the other supple, to waterproof a substrate and U.S. Pat. No. 3,423,232 to Reinhard et al. which discloses coating flat substrates with aqueous dispersions including 80-98% vinylidene chloride polymers as a subcoating and top coating.
U.S. Pat. No. 3,306,766 to Hathaway et al. discloses a resin coated packaging product, preferably a paper based sheet, having the exposed surface thereof coated with a haloethylene polymer resin, such as saran, and an intermediate flexible foundation coating of extruded ethylene-lower alkyl acrylate copolymer resin. The haloethylene polymer resins, e.g. saran, are resistant to the passage of water vapor and include at least 60% by weight of polyvinylidene chloride resins.
From the prior art mentioned it is seen that coatings which include vinylidene chloride copolymers to provide a moisture barrier are known, however, the prior art does not provide a method for directly applying these coatings to a porous substrate. It would be appreciated that advantage over known applications would be obtained by providing wax free aqueous coatings directly applied to a substrate surface to impart water and water vapor resistance properties comparable to conventional polyethylene or wax coatings but are repulped and recycled more readily. The present invention is directed to the provision of such recyclable and repulpable coatings to produce a coated paper product for use as ream wrap. The water-based coatings of the invention provide an alternative to conventional polyethylene coatings and wax coatings and an advantage over the prior art since the coated paper can easily be repulped without special flotation equipment, which is needed when repulping polyethylene film. The water-based coatings disperse in water, allowing the paper fibers to be easily reclaimed for reuse. The invention coatings, unlike wax-coatings, are repulped and recycled along with office wastepaper to produce a high grade white paper.
Accordingly, it is a broad object of the invention to provide a recyclable and repulpable coated paper stock comprised of a substrate coated with a base coat and at least one additional coat over the base coat, both of which are wax free water-based polymeric dispersions.
An object of the invention is to provide a recyclable and repulpable coated paper stock which is formed into a package, container or label.
A more specific object of the invention is to provide a recyclable and repulpable coated paper stock, for use as ream wrap, having water resistance, grease resistance and moisture vapor barrier characteristics.
A specific object of the invention is to provide a coated paper stock that is readily recycled without dependence on special equipment for repulping.
A more specific object of the invention is to provide a coated paper stock that is readily repulped and recycled along with office waste paper to produce a high grade white paper.